In conventional combine harvesters crop material is fed between a threshing cylinder and an associated threshing concave, which extend transversely to the direction of combine travel. In this case, the crop is threshed over a comparatively short distance. Axial flow machines, on the other hand, use one or more longitudinally arranged rotors and associated concaves. Here, crop material is subjected to a much longer threshing and separating action than in a conventional machine and therefore, the efficiency of axial flow machines is greater because a higher degree of separation is reached and the grain losses are reduced. Commonly, axial flow combines are popular in regions with a continental climate, where the crops to be harvested ripen well and contain hardly any green parts at the time of the harvest. However, when the crop contains green material, such a unit is particularly prone to plugging by slugs of accumulated crop material between the rotor and the concaves.
Various means have been provided onto the rotor to optimise the crop flow along the rear portion of the threshing and separating unit and to improve the rotor performance under adverse conditions. U.S. Pat. No. 4,936,810, for example, proposes using thinning elements in the form of generally radially extending fingers to smoothen the layer of crop material which is advancing along the concaves. The fingers co-operate with conventional longitudinal bars on the rotor body to move the crop layer along a helical path and to loosen the same. This system is still optimal when harvesting dry crops, but too often slugs occur when handling greener material.
U.S. Pat. No. 5,376,047 discloses a rotor equipped with a multitude of rectangular blades which can be distributed along the surface of the rotor in order to optimise the crop flow. For a particular crop and a particular crop condition, a blade distribution may be found which is optimal with respect to threshing and separating efficiency and/or plugging risks, but such experimentation is not within reach of the ordinary operator.
In U.S. Pat. No. 4,178,943 a rotor is shown equipped with generally transverse fins behind the threshing section. The separation capacity of this embodiment is limited because of the restrained action of the fin heads on the layer of crop material. The grain losses at the end of the separation section may raise to unacceptable levels, unless the rate of incoming material is reduced by lowering the ground speed of the combine harvester.